Daily solar radiation is an important element in the application of solar energy. Measuring solar radiation requires advanced tools and equipment. Hence, solar radiation measured data are not always available in the all the meteorological stations. Generally it needs to be estimated by empirical models based on frequently available meteorological records such as hours of sunshine or temperature. This paper evaluates the behavior of five empirical models based on the difference between maximum and minimum temperatures (the models of Bristow & Campbell, Hargreaves, Samani, Chen and Li). With statistical error tests, the performance of the models is validated by comparing together against the measured data at 12 meteorological stations in Iran located in four region climate humid, semi-humid, semi-arid and arid. Results show that the models are more accurate in the arid regions as compared to humid regions. Hence, these models can be recommended for estimating daily solar radiation in arid regions where only air temperature data are available in Iran.

For decreasing the amount of air pollution and green gas emission and saving fossil fuels resource, one of the ways is extending renewable energy utilization. Hence, this yields to growth and development of Photovoltaic systems. Nowadays due to increasing electrical energy requirements and ability to privately providing required energy, the use of solar energy and its electrical power creativity by means of PV systems expanded. In this study an electricity network independent system designed to provide electricity for a house around Karaj at a certain season of the year. The energy demand for this house is 4320 Watt-hours. For providing this amount of energy, 830 watt photovoltaic array, a 1500-watt inverter, a charge controller with a capacity of 40 amp and 24 volt battery with 600 amp hour capacity is needed. The cost needed for this project estimated about 103700000 Rials. PVsyst software used to calculate system losses and finally environmental impact of system compared with conventional systems.